Air conditioning systems for vehicles are generally equipped with an air conditioner and an air blower. To operate such a system, a main switch for starting and stopping the air conditioner and a selector switch for changing the flow of air supplied by the blower from one level to another are provided. The selector switch typically takes the form of a sliding switch, and has a stop position at which the blower is stopped. When the selector switch assumes this stop position, if the air conditioner is still in operation, the cooling coil will frost. Therefore, whenever the blower is stopped, the air conditioner is required to be stopped.
In order to fulfill this requirement, a composite switch is used in which an air flow selector switch interlocks with a main switch. Conventional composite switches of this kind are shown in FIGS. 1-3(C).
Referring first to FIG. 1, there are shown a main switch 1 and a selector switch 2. The main switch 1 is of a so-called push-pull type and serves to start and stop the air conditioner of a vehicle. The main switch 1 has an actuating member 3 which is provided with a heart-shaped grooved cam 3a. A ball 4 is biased into the cam 3a by a spring (not shown). Usually, the actuating member 3 is caused to protrude in the direction indicated by the arrow A by the action of the spring. Under this condition, the main switch is open. When the actuating member 3 is pushed in the direction indicated by the arrow B, the contacts complete an electrical circuit. At this time, the ball 4 slides along the grooved cam 3a until it comes to a halt in lock position .alpha., whereupon the actuating member 3 keeps the contacts in that condition. Then, if the actuating member 3 is pushed further, the ball 4 moves out of the lock position .alpha., and the action of the spring restores the actuating member 3 in the direction indicated by the arrow A to open the switch. The ball 4 is only allowed to move laterally in the drawing by means of a slot 5a formed in a limiting member 5.
The selector switch 2 comprises a casing 6 made from an insulating material and a cover 7 made of a metal plate. The casing 6 cooperates with the cover 7 to form a frame, in which an operating member 8 made from an insulating material can slide. A sliding contact 8a is held to the operating member 8. The casing 6 has one surface 6a to which a plurality of fixed contacts (not shown) are securely fixed. An actuating lever 9 has its front end 9a engaged in the operating member 8, and is rotatable about a pivot 10.
When the actuating lever 9 is turned in the direction indicated by the arrow C, the operating member 8 is shifted to the left as viewed in the figure to bring the sliding contact 8a into contact with the contact on the left side. This changes the flow of air supplied by the air blower to a higher level. If the lever 9 is gradually turned in the direction indicated by the arrow D from that position, the operating member 8 is moved to the right to bring the sliding contact 8a into contact with the other fixed contacts in turn. Thus, the flow of air supplied by the blower is reduced in stepwise fashion. When the lever 9 is fully turned in the direction indicated by the arrow D, the blower stops. At this time, the operating member 8 pushes one end 5b of the limiting member 5, which is usually retained in the position shown in FIG. 1 by the spring. Then, the limiting member 5 is moved to the right (see FIG. 2), and the slot 5a in the limiting member 5 pushes the ball 4 to the right. Accordingly, even if the actuating member 3 of the main switch 1 is locked in a position along the direction indicated by the arrow B, i.e., the switch is closed, the movement of the limiting member 5 moves the ball 4 out of the lock position .alpha. in the cam 3a. Immediately thereafter, the actuating member 3 returns in the direction indicated by the arrow A to open the main switch 1, thus stopping the air conditioner.
Referring next to FIGS. 3(A)-3(C), there is shown another prior art composite switch which comprises a main switch 1 and a selector switch 2. The switch 2 is the same as the selector switch 2 shown in FIG. 1. The main switch 1 has an actuating member 3 that is formed with a heart-shaped grooved cam 3a in which the front end 11a of a pin 11 is inserted. When the front end 11a of the pin 11 is retained in position .alpha. in the cam 3a, if the actuating member 3 is turned in the direction indicated by the arrow B, it is locked. The pin 11 is biased into the cam 3a by a spring 12. A limiting member 13 has an inclined surface 13a lying below the pin 11. When the actuating lever 9 of the selector switch 2 is turned in the direction indicated by the arrow D to stop the blower, the operating member 8 causes the limiting member 13 to move to the right. Then, the inclined surface 13a pushes the pin 11 upward. Thus, even if the front end 11a of the pin 11 is engaged in the lock position .alpha., when the pin is raised, it comes out of the lock position. Then, the actuating member 3 returns in the direction indicated by the arrow A, opening the main switch 1.
In the conventional composite switches described above, when the operating member 8 of the selector switch 2 is moved in one direction, the lock member 4 or 11 of the main switch 1 is forced to move toward the direction to open the switch 1. That is, the actuating member 3 itself of the main switch 1 is fully restored in the direction to open the switch. Accordingly, in order to restart the air conditioner, the actuating lever 9 of the selector switch 2 must be actuated to start the blower. Further, the actuating member 3 of the main switch 1 must be pushed again. When a person is driving the vehicle, it is cumbersome for him to perform these operations. In addition, he tends to forget to depress the main switch 1. Furthermore, since mechanical action is employed to open the main switch 1, a complicated mechanism is needed to unlock the main switch. Also, there is the possibility of malfunction.